CHRIST IS RISEN!
When someone says they believe in and go only by the Bible (I used to be one so I know) what they really mean is that they believe in and go only by their interpretation of the Bible. If they really believed the Bible they would accept that the Bible forbids private interpretation and requires us to accept the Church as the pillar and gound of the Truth and to accept the written and unwrritten Apostolic Tradition.
Interesting point...that you used to be one. I would think that you would understand him better, since you were in his shoes once. What happened to you that opened your eyes?
The original sin of Adam was an insistance on a personal and private interpretation of God's revealed will. Since then, it has been one of Satan's favorite tools.
No. The original sin was refusing to repent for their disobedience. God already knew what they were going to do. God knows that we, as the created, will be tempted and fall. God called to Adam, in the Garden, three times, giving him the chance to repent. But, He already knew that Adam would not repent. That is why He had already planned for Christ to come to us and be sacraficed for us...to break the power that satan was given over us because of the choice of the free will of Adam and Eve. Just as Christ asked Ap. Peter, three times, if he loved Him. Ap. Peter repented for his lack of faith. God knew what satan was planning. satan's favorite tool is pride, which leads to many paths and one of them is personal interpretation of the Holy Scriptures.